Phase 1 Clinical Trial of Adoptive Immunotherapy for Acute Myelogenous Leukemia and Myelodysplastic Syndrome, Using Gene-Modified Autologous Lymphocytes Expressing WT1-Specific T-Cell Receptor

Elderly patients (pts) with acute myelogenous leukemia (AML) and high-risk myelodysplastic syndrome (MDS) particularly who are ineligible for allogeneic hematopoietic stem cell transplantation (allo-HSCT) and have disease relapse after allo-HSCT still have a poor prognosis. Thus, the development of novel treatment option providing higher response rate and prolonged survival time for those patients still remains an unmet need. Because not a few clinical and preclinical studies have described a promising value of Wilms Tumor 1 (WT1), a leukemia-associated antigen as a therapeutic target of antileukemia immunotherapy, we conducted a clinical study of novel adoptive immunotherapy using gene-modified autologous lymphocytes expressing WT1-specific T-cell receptor (TCR) for the treatment of refractory AML and high-risk MDS.

A multicenter phase 1 study was conducted to assess feasibility, safety and preliminary antileukemia reactivity of patient-derived gene-modified lymphocytes expressing WT1-specific TCR. Antigen-specific TCR-gene transfer may cause a serious autoimmune disease mediated by mispaired TCR between introduced and endogenous TCR α/β chains. To avoid that, we established a retroviral vector system encoding siRNAs for endogenous TCR genes (siTCR vector). We conducted a first-in-human clinical trial employing this siTCR vector. After given written informed consents, mononuclear cells were collected from at most 200ml of peripheral blood (PB) from each patient. Then, proliferating lymphocytes pre-cultured with IL-2, anti-CD3 antibody and RetroNectin^TM were infected with a retroviral vector, MS3-WT1-siTCR composed of DNAs encoding WT1_235-243/HLA-A*24:02 complex specific TCR-α/β chains and siRNAs against endogenous TCR genes. Expanded gene-modified lymphocytes (WT1-siTCR/T cells) in additional culture for 13-14 more days were harvested and frozen until use. Eligibility included HLA-A*24:02 positive pts with refractory AML or high-risk MDS, > 20 y.o, ineligible for allo-HSCT and performance status of 0 to 2. WT1-siTCR/T cells were intravenously infused twice on days 0 and 28. Heteroclitic WT1_235-243 ninemer peptide (300mg) emulsified with Montanide^TM was given subcutaneously on day 2 and 16 after the second infusion. Besides safety assays, kinetics of WT1-siTCR/T cells in PB, immunological responses and residual leukemia burden determined by qRT-PCR for WT1 mRNA were serially measured until day 58 since the first infusion.

Among 12 pts enrolled, 8 pts (5 AML, 3 MDS) with a median age of 68.5 y. received study treatment. Three pts received 2x10⁸ cells/ infusion (cohort 1), 3 received 1x10⁹ cells/ infusion (cohort 2), and 2 received extra-cohort doses. Median follow-up time after the first infusion was 257 days (as June 13, 2016). At the first infusion, all pts contracted progressive disease. Circulatory WT1-siTCR/T cells retaining the target reactivity appeared immediately after each infusion, peaked between 1 to 3 days, and declined thereafter. WT1 peptide vaccination did not seem to affect the transition of infused cells. Values of WT1 mRNA in PB were transiently suppressed in all pts and declined in 4 pts thereafter. Clinical outcomes included one with stable disease and 2 pts with partial remission (PR). In one with PR, the epitope-spreading phenomenon was suggested. In all pts, no serious adverse events associated with infused WT1-siTCR/T cells were observed.

Adoptive transfer of autologous WT1-siTCR/T cells was feasible and safe. Although the persistence of infused WT1-siTCR/T cells was limited, infused WT1-siTCR/T cells at least seemed to be involved in the antileukemia reactivity.